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FZJ-2018-00432

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Die Bestimmung von Verankerungskräften für Flußlinien in Supraleitern durch Neutronenbeugung

Lippmann, G. (Corresponding author)FZJ*

1975
Kernforschungsanlage Jülich, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/16568

Report No.: Juel-1214

Abstract: In this paper neutron diffraction experiments by flux line lattices in Niobium samples at 4.2 K are reported. The samples cantained non-superconducting Nb$_{2}$N-precipitates in variaus cancentratians which act as pinning centers. The pinned flux lines are na langer exactly parallel ta each ather as they would be in an ideal type-II supercanductar but are tilted by small angles with respect to the external field. This angular tilt results in a broadening af the Bragg-reflections in directian af the flux lines which is measured by recording racking-curves. The characteristic parameter af the racking-curves is their full width at half maximum; it varied with precipitate concentratian and flux density and ranged from 6' to 250'. Labusch (1975) has derived a new theary which carrelates the measured halfwidths to the pinning force exerted on one flux line by one pinning center. By means of this theory the mean square values $\langle$f$^{2}\rangle$$^{1/2}$ of the interactionforces cauld be determined more directly than previously where in mast cases pinning force densities had ta be measured by macroscopic methods. The interactianfarces coincided within experimental errar far all samples even thaugh their precipitate concentrations varied by an arder af magnitude. At a reduced flux density of 0.5 a value for $\langle$f$^{2}\rangle$$^{1/2}$ of (18 $\pm$ 4) $\cdot$ 10$^{-11}$ N has been obtained. A comparison has been made between the mean square interaction forces $\langle$f$^{2}\rangle$$^{1/2}$ and the maximum interaction forces K$_{o}$ determined from pinning force densities P$_{V}$ · P$_{V}$ has been measured on the system $\underline{Nb}$Ta + Nb$_{2}$N-precipitates by Antesberger (1973) and an one of the samples used in these experiments by Fuhrmans (1975). An agreement within a factor twa has been found between $\langle$f$^{2}\rangle$$^{1/2}$ determined from the tilt angles and K$_{o}$ determined from P$_{V}$ -measurements. In comparing the two completely different methads one has to take into consideration, hawever, that the averaging procedure inherent to the homogeneaus flux density distributian used in the neutron experiment yields a mean square value for the interaction force which should always be smaller than the maximum interaction force otained by the macroscopic methods. The deviation from the proportionality between $\langle$f$^{2}\rangle$$^{1/2}$ and K$_{o}$ becomes large specially at low flux densities. This comparison seems to prove that the theory for the determination of K$_{o}$ from P$_{V}$ describes the behaviour of fux lines in pinned superconductors in the right way. A higher absolute accuracy for both methads depends an a more homogeneous distribution of the pinning centers in the sample and an a more precise determination of their concentration by applying neutron small angle scattering or metallurgical techniques.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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